sanitize the bad codeserver name before outputting the error message for security

Review at http://gwt-code-reviews.appspot.com/1483804

Review by: cromwellian@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10458 8db76d5a-ed1c-0410-87a9-c151d255dfc7